Codigo elemental mathematica

Codigo MATHEMATICA para dibujar, calcular gradiente, Laplaciano

ClearAll["Global`*"]
"Dada la funcion 2 variables"
g[x, y] = (x^2 + y^2)
"derivadas parciales";
C1 = D[g[x, y], x];
C2 = D[g[x, y], y];
"Nico gradiente que le duele el diente"
G1 = {C1, C2}
"Laplaciano"
Laplacian[g[x, y], {x, y}]
"Max"
Maximize[g[x, y], {x, y}]
Maximize[{g[x, y], 
1 <= x + y <= 2 && 1 <= x - y <= 2 && x - y == 3}, {x, y}]
Plot3D[(x^2 + y^2), {x, -30, 30}, {y, -20, 0}, Mesh -> All]